This invention relates generally to automotive diagnostic equipment and particularly to computer-based equipment for testing and evaluating internal combustion engines.
It is well known in the art of automobile engine testing to utilize computer-based equipment. One such apparatus, identified as the Sun Electric Corporation 2001, is described and claimed in U.S. Pat. No. 4,125,894 issued Nov. 14, 1978, which is hereby incorporated by references. With such equipment, selected engine test signals are gathered by suitable probes connected to the engine. The analog test signals and data are manipulated, processed and compared with factory data for the particular engine or vehicle type and displayed for use of the service technician. Some systems also provide print outs of the test results with evaluation.
One popular diagnostic tester is the recently introduced Sun Electric Corporation Model MCA 3000. That system, includes an IBM compatible PC in addition to the test apparatus that enables the service technician to rapidly acquire and process signals and data from the engine under test. The high speed of the MCA 3000 is due largely to its Data Acquisition System (DAS). With the DAS, analog data obtained from the engine is converted by an analog to digital (A/D) converted and stored in an A/D Random Access Memory (RAM) without the intervention of the main controller. The dual ported A/D RAM that is used for this purpose is the subject of application Ser. No. 148,974. The system controller in the preferred embodiment is an IBM compatible PC having 640 kilobytes of system memory. An additional 118 kilobyte RAM memory is plugged into a card slot normally reserved for a RAM cartridge. It is dual ported, enabling both the DAS and system microprocessor to access it. In accordance with the present invention, the data is stored in the form of digital words and the initiations of certain events are identified by suitable flags added to the data as it is loaded into the A/D memory. In the preferred embodiment the flags are positioned in the higher order bits of the digital word that do not convey magnitude information, i.e. that are beyond the range of magnitudes encountered. It should be apparent however that the flags may occupy any known locations in the digital word with suitable changes in processing. The flags are detected and used to locate and identify the data in the A/D memory. Application Ser. No. 148,972 describes and claims a novel system of identification and removal of the flags in which the data is replaced in memory with the flags reset. In that arrangement the system controller constructs a pointer array in system memory that identifies the addresses of the data in A/D memory. The flags in the data enable rapid access to and retrieval of the data for processing, display etc., in accordance with the selected tests.
The present invention is specifically concerned with the flag generation system for identifying, for ready retrieval, the engine test data. It is thus independent of the inventions in the above-mentioned copending applications, although their use with the invention produces significant benefits.